162
FXUS65 KBYZ 200656
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
1256 AM MDT WED MAY 20 2026
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING;
MAIN RISKS ARE SMALL HAIL, ERRATIC WIND GUSTS AND LOCALIZED
MODERATE RAINFALL.
- COOL AND WET WEATHER SYSTEM BRINGS WIDESPREAD RAIN AND SNOW IN
THE MOUNTAINS ABOVE 7000 FEET, TONIGHT THROUGH THURSDAY.
- OVER A HALF INCH OF PRECIP IS EXPECTED ALONG SOUTHERN MOUNTAINS
AND FOOTHILLS (>75% CHANCE). NORTH ASPECTS OF SOUTHERN MOUNTAINS
WILL SEE 6" OR MORE OF SNOWFALL (80% CHANCE). THE OPENING OF THE
BEARTOOTH HIGHWAY ON FRIDAY MAY BE IMPACTED.
- WARMING TREND FRIDAY THROUGH EARLY NEXT WEEK.
DISCUSSION
THROUGH NEXT TUESDAY...
WATER VAPOR IMAGERY SHOWS A DISTINCT SHORTWAVE DROPPING THRU BC/AB
IN NORTHERLY FLOW ALOFT, DOWNSTREAM OF A STRONG UPPER LEVEL RIDGE
OFF THE PACIFIC COAST. THIS WAVE IS EXPECTED TO FORM A WEAK MID
LEVEL LOW AS IT REACHES SOUTHERN AB TOMORROW, AND IS OUR PRIMARY
WEATHER-MAKER OVER THE NEXT 36HRS. THIS BEGINS WITH INCREASED
T-STORM POTENTIAL THIS AFTERNOON AND EVENING, WITH HIGH RES MODELS
SUGGESTING DEVELOPMENT BEGINNING IN OUR W/NW AROUND NOON (EARLY
START PER THE INCREASING SYNOPTIC SCALE ASCENT). INSTABILITY IS
VERY MODEST (100-400 J/KG) BUT THE TALL/SKINNY CAPE W/ RELATIVELY
LOW FREEZING LEVELS SHOULD SUPPORT SMALL HAIL, ALONG WITH ERRATIC
WIND GUSTS AND LOCALIZED MODERATE RAINFALL. HEADS UP TO THOSE W/
OUTDOOR PLANS IN THE EVENING.
A COLD FRONT ARRIVES FROM THE NORTH IN THE LATE AFTERNOON (PRE-
FRONTAL TEMPS SHOULD REACH THE 60S TO LOW 70S) AND THE DIURNAL
CONVECTION WILL EVOLVE TO A PRECIP EVENT TONIGHT THRU THURSDAY. AS
ENERGY DIGS THRU WESTERN MT INTO SOUTHEAST ID, UPSLOPE N=NE WINDS
WILL DEEPEN AND THUS PRECIP WILL BECOME MOST WIDESPREAD OVER OUR
SOUTHERN UPSLOPE AREAS, GRADUALLY SHIFTING EASTWARD THRU THE DAY
TOMORROW. CHANCES OF AT LEAST 0.50" OF RAIN ARE HIGH IN THESE
UPSLOPE AREAS (>75%) BUT EVEN BILLINGS-HARDIN COULD SEE A HALF
INCH (50% CHANCE). LESSER AMOUNTS WILL FALL OVER THE NORTH AND
EAST OF ROSEBUD COUNTY (0.05-0.25"). WILL NEED TO MONITOR FOR A
POTENTIAL AXIS OF ENHANCED FRONTOGENESIS AS THE TROF PIVOTS TO OUR
WEST, WHICH ALONG WITH THE UPSLOPING COULD PRODUCE OVER AN INCH
OF PRECIP ON THE NORTH ASPECTS OF THE BEARTOOTHS/PRYORS/NORTHERN
BIGHORNS...AND AMONG THESE AREAS LATEST MODELS SHOW WESTERN BIG
HORN COUNTY HAS THE GREATEST POTENTIAL. IN ADDITION TO THE PRECIP,
SNOW WILL FALL ABOVE 7KFT WITH SEVERAL INCHES OF ACCUMULATION IN
THE AFOREMENTIONED UPSLOPE AREAS. THE BEARTOOTH HWY IS SCHEDULED
TO OPEN FRIDAY BUT THERE MAY BE SOME PLOWING NEEDED FIRST. LOWER
ELEVATION HIGH TEMPS THURSDAY WILL BE COOL (UPPER 40S AND 50S)
BUT EXPECT A RETURN TO THE 60S FRIDAY AS THE SYSTEM EXITS AND IS
REPLACED BY RISING HEIGHTS. ONE FINAL NOTE, AS THE SYNOPTIC
FORCING SHIFTS EAST THURSDAY THERE SHOULD BE ENOUGH INSTABILITY
FOR THE DEVELOPMENT OF SCATTERED DIURNAL SHOWERS ON THE BACK SIDE
OF THE TROF.
FRIDAY THROUGH THE WEEKEND WILL TREND WARMER AND BE MOSTLY DRY,
BUT THERE MAY BE ENOUGH WEAK SHORTWAVE ACTIVITY THRU THE BACKED
ZONAL FLOW FOR ISOLATED DIURNAL CONVECTION, AT LEAST OVER THE
MOUNTAINS. LOOK FOR TEMPS BACK TO THE 70S SATURDAY AND INTO THE
LOW-MID 80S SUNDAY.
THE FIRST HALF OF NEXT WEEK WILL SEE THE NEXT PACIFIC TROF BEGIN
TO MOVE INLAND IN SOME FASHION. CLUSTER ANALYSES SHOW HIGH SPREAD
IN POTENTIAL SOLUTIONS WITH THIS TROF, RANGING FROM AN OPEN WAVE
ACROSS THE NORTHERN ROCKIES TO A DEEP LOW FORMING OVER THE SW
CONUS. IMPOSSIBLE TO DETERMINE AT THIS TIME, BUT GENERALLY
SPEAKING LOOK FOR A WARM START TO THE NEXT WORK WEEK (80S) THEN
MODEST COOLING AND INCREASING CHANCES OF SHOWERS/T-STORMS PER THE
ADVANCING TROF. IF ANOTHER DYNAMIC LOW FORMS TO OUR SW/W IT MAY
ALLOW FOR A PUSH OF PLAINS MOISTURE AND GREATER INSTABILITY FOR
POTENTIAL T-STORMS. SOMETHING TO MONITOR.
JKL
AVIATION
VFR WILL PREVAIL THROUGH THE FIRST HALF OF TODAY WITH MID CLOUDS
ON THE INCREASE FROM AN APPROACHING WEATHER SYSTEM. AN ASSOCIATED
COLD FRONT WILL DROP THROUGH THE AREA THIS AFTERNOON AND EVENING
BRINGING INCREASING CHANCES FOR SHOWERS AND WEAK THUNDERSTORMS.
WIND GUSTS UP TO 25 KTS ARE POSSIBLE WITH THE FRONTAL PASSAGE, AND
THUNDERSTORMS WILL BE CAPABLE OF GUSTY AND ERRATIC WINDS TO 30
KTS, SMALL HAIL AND BRIEF DOWNPOURS. MVFR CONDITIONS ARE POSSIBLE
WITH THE SHOWERS/THUNDERSTORMS, WITH SHOWERS BECOMING MORE
PROMINENT THIS EVENING, SPREADING EAST OVERNIGHT. MOUNTAINS WILL
BECOME OBSCURED THIS AFTERNOON AND EVENING DUE TO RAIN/SNOW. STP
PRELIMINARY POINT TEMP/POPS
TDY THU FRI SAT SUN MON TUE
-------------------------------------------------------
BIL 068 043/056 039/069 045/079 051/085 053/089 054/082
4/T +8/T 10/U 00/U 00/U 01/U 12/T
LVM 063 036/054 032/067 040/076 046/081 048/084 048/074
4/T +8/T 10/B 00/U 11/U 22/T 15/T
HDN 070 041/057 037/071 040/079 046/085 049/089 051/083
2/T 99/T 10/U 00/U 00/U 00/U 12/T
MLS 072 044/062 040/069 042/078 048/084 051/090 055/086
2/T 66/W 21/U 00/U 00/U 00/U 11/N
4BQ 071 042/058 040/066 041/076 047/083 051/089 056/086
2/T 26/T 52/W 00/U 00/U 00/U 01/N
BHK 072 038/065 038/066 038/076 047/083 050/088 055/086
2/T 36/T 63/W 10/U 00/U 00/U 01/N
SHR 067 038/049 033/064 035/073 040/081 043/087 045/082
2/T 2+/T 51/U 01/U 01/U 00/U 02/T
BYZ WATCHES/WARNINGS/ADVISORIES
MT...NONE.
WY...NONE.
WEATHER.GOV/BILLINGS
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